Amplifying Optical Electromagnetic Wave Concentrator

ABSTRACT

An amplifying optical electromagnetic wave concentrator includes an amplification focusing device and a receiver. The amplification focusing device focuses an incident optical electromagnetic wave on the receiver. The amplification focusing device is doped with active components and is subjected to an excitation wave that causes the active components to pass to an energy level such that interaction between the incident electromagnetic wave and the active components causes the active components to pass to a lower energy level and causes emission, towards the receiver, of at least one photon having the same wavelength as the incident electromagnetic wave. The focused photon or photons form an amplified wave of the incident electromagnetic wave.

RELATED APPLICATIONS

The present application is based on, and claims priority fromInternational Application Number PCT/EP04/006421, filed Jun. 14, 2004,the disclosure of which is hereby incorporated by reference herein inits entirety.

FIELD OF THE INVENTION

The invention concerns an amplifying optical electromagnetic waveconcentrator. It also concerns a device for receiving an opticalelectromagnetic wave comprising a plurality of such amplifyingconcentrators. It finds an application in fields requiring sensitivedetection of electromagnetic radiation. In particular it finds anapplication in the fields of telecommunications by atmospheric opticalconnections and local wireless networks by optical connection of theinfrared type.

BACKGROUND OF THE INVENTION

Communications by optical connection, in particular by infraredconnection, take place between a transmitter that transmits the opticalsignal and a receiver that receives it. Because of losses, the energy ofthe optical signal transmitted by the transmitter is not entirelyreceived by the receiver and the energy of the signal received may below. In order to compensate for these losses and increase the energy ofthe received signal, a concentrator is placed in front of the receiver.This concentrator captures the beams that pass in the vicinity of thereceiver and redirects them to the latter whilst focusing them, thusaffording an increase in the energy of the received signal byconcentration on the receiver.

Such an optical electromagnetic wave concentrator is described by XinYang in an article published by “SPIE Proceedings” of December 2002(Proceedings of SPIE—Volume 4873—Optical Wireless Communications V, EricJ. Korevaar, Editor, December 2002, pp 71-78) under the title“Simulation of impulse response on IR wireless indoor channel withconcentrator”.

The concentrator has the shape of a truncated sphere placed in front ofa detector, the radius of which is greater than the radius of thedetector, thus making it possible to redirect the incident beams thatare outside the field of the detector towards the detector. This type ofconcentrator gives satisfaction if the energies of the various opticalbeams received by the concentrator are not too low and if theconcentration of the beams makes it possible to achieve a certain energylevel affording good detection of the signal; in particular the totalenergy must make it possible to have an advantageous signal to noiseratio.

One object of the present invention is to propose an amplifying opticalelectromagnetic wave concentrator that does not have the drawbacks ofthe prior art.

SUMMARY OF THE INVENTION

To this end, an amplifying optical electromagnetic wave concentratorcomprising at least one amplification focusing device and a receiver isproposed, the amplification focusing device being adapted to focus anincident optical electromagnetic wave on the receiver. The amplificationfocusing device is produced from a material doped with active componentsand is subjected to an excitation wave so as to make the activecomponents pass to an energy level, such that the interaction betweenthe incident electromagnetic wave and the said active components causesthe said active components to pass to a lower energy level and causesthe emission of at least one photon having the same wavelength as theincident electromagnetic wave towards the receiver, the focused part andthe photon or photons emitted constituting an incident amplified wave ofthe incident electromagnetic wave.

The incident wave received by the focusing device is therefore amplifiedand the wave thus amplified makes it possible to achieve signal valuessufficient to allow a good detection of the signal.

Advantageously, a variation of the power of the excitation wave in onedirection causes a variation of the power of the incident amplified wavein the same direction. The power of the incident amplified wave thatcirculates in the waveguide can thus be controlled by the power of theexcitation wave.

Advantageously, the amplification focusing device is spherical orhemispherical.

According to a first embodiment, the receiver is a waveguide adapted toconduct the incident amplified wave.

According to a variant of the first embodiment, the waveguide is anoptical fibre.

Advantageously, the end of the optical fibre facing the amplificationfocusing device is provided with a microlens.

Advantageously, the amplifying concentrator comprises a tubular devicein which the optical fibre is positioned and at the end of which theamplification focusing device is placed.

According to another variant of the first embodiment, the waveguide is aplanar guide.

According to a second embodiment, the receiver is an optical toelectrical converter.

Advantageously the excitation wave is a laser beam.

Advantageously the excitation wave is emitted towards the amplificationfocusing device from a waveguide adapted to conduct the excitation wave.

Advantageously, according to the first embodiment, the waveguide adaptedto conduct the excitation wave is the waveguide adapted to conduct theincident amplified wave.

The invention also proposes a device for receiving an incident opticalelectromagnetic wave comprising a plurality of amplifying concentratorsaccording to one of the preceding embodiments.

Advantageously the amplification focusing devices of the plurality ofamplifying concentrators are distributed over a substantiallyhemispherical surface.

Advantageously the reception device comprises an optical adder connectedto the plurality of receivers and adapted to add the energies of thesignals issuing from each receiver.

Advantageously the reception device comprises an optical coupler or ademultiplexer connected to the output of the optical adder and intowhich the excitation wave is injected.

Advantageously the reception device comprises a device for measuring theenergy of the wave output from the optical coupler or from thedemultiplexer and the measuring device is adapted to control the powerof the excitation wave.

Advantageously the reception device comprises an optical demultiplexerinto which the excitation wave is injected and the outputs of which areconnected to the plurality of wave guides adapted to conduct theexcitation wave.

Advantageously the reception device comprises a device for measuring theenergy of the electrical signal output from the electrical adder and themeasuring device is adapted to control the power of the excitation wave.

The characteristics of the invention mentioned above, as well as others,will emerge more clearly from a reading of the following description ofan example of an embodiment, the said description being given inrelation to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a drawing of an amplifying optical electromagnetic waveconcentrator according to a first embodiment of the invention;

FIG. 2 is a drawing of a reception device comprising a plurality ofamplifying electromagnetic wave concentrators according to the firstembodiment of the invention;

FIG. 3 is a drawing of an amplifying optical electromagnetic waveconcentrator according to a second embodiment of the invention;

FIG. 4 is a drawing of a reception device comprising a plurality ofamplifying electromagnetic wave concentrators according to the secondembodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 is a drawing of an amplifying optical electromagnetic waveconcentrator 100 according to a first embodiment and FIG. 3 depicts anamplifying optical electromagnetic wave concentrator 300 according to asecond embodiment.

Each amplifying concentrator 100, 300 comprises at least oneamplification focusing device 106 and respectively a receiver 102, 304.The amplification focusing device 106 is adapted to focus an incidentoptical electromagnetic wave 116 onto respectively the receiver 102,304.

The amplification focusing device 106 is produced from a material dopedwith active components 108 and is subjected to an excitation wave 112that makes the active components 108 pass to a so-called higher energylevel. This so-called higher energy level is such that the interactionbetween the incident electromagnetic wave 116 and the said activecomponents 108 causes the said active components 108 to pass to a lowerenergy level and causes the emission of at least one photon having thesame wavelength as the incident electromagnetic wave towardsrespectively the receiver 102, 304.

The active components 108 are said to be adapted to the wavelength ofthe incident electromagnetic wave 116, that is to say they emit a photonhaving the same wavelength as that of the photons of the incidentelectromagnetic wave 116, when they are illuminated by the incidentelectromagnetic wave 116. There is then a photomultiplication of thepart of the incident electromagnetic wave 116 picked up by theamplification focusing device 106, which increases the energy level ofthe wave received and then transmitted respectively to the receiver 102,304.

The focused part of the incident optical electromagnetic wave 116 andthe photon or photons emitted then constitute an incident amplified wave114 of the incident wave 116.

In other words, the incident optical electromagnetic wave 116illuminates the amplification focusing device 106, which also receivesthe excitation wave 112 and transmits the incident amplified wave 114 inthe direction respectively of the receiver 102, 304.

The active components 108 can be of the atom, atomic ion, molecule,molecular ion or other type.

The amplification focusing device 106 is therefore illuminated by theincident optical electromagnetic wave 116 that issued from a transmitterand makes it possible to concentrate and focus the part of theelectromagnetic wave issuing from the transmitter and received by theamplification focusing device 106 towards respectively the receiver 102,304. The fitting of a doped material also allows an amplification of thesignal transmitted from the amplification focusing device 106 torespectively the receiver 102, 304.

According to the first embodiment depicted in FIG. 1, the receiver canbe a waveguide 102 adapted to conduct the incident amplifiedelectromagnetic wave 104 thus concentrated and focused towards aprocessing device that will be explained below. The use of a waveguide102 makes it possible to offset the processing device from theamplification focusing device 102, unlike the prior art, which makes itnecessary to mount the detector behind the concentrator.

The waveguide 102 can be an optical fibre at the end of which amicrolens 104 can be mounted, opposite the amplification focusing device106, in order to focus the amplified beams issuing from theamplification focusing device 106 towards the centre of the opticalfibre 102.

In the particular case shown in FIG. 1, the amplification focusingdevice 106 in the form of a sphere and the waveguide 102 in the form ofan optical fibre are placed inside a tubular device 110, for example inthe form of a silica tube, which facilitates the fitting of the opticalfibre 102 with respect to the amplification focusing device 106. Theoptical fibre 102 is positioned in the tubular device 110 and theamplification focusing device 106 is placed at the end of the tubulardevice 110. In addition, the tubular device 110 allows the adjustment ofthe device between the end of the optical fibre 102 and theamplification focusing device 106, in order to position this end at theregion where the maximum concentration of energy is situated, andmoreover it prevents to the maximum possible extent the losses of energybetween the amplification focusing device 106 and the optical fibre 102by keeping the beams issuing from the amplification focusing device 106between its internal walls.

The waveguide 102 can also be a planar guide on which for examplehemispherical alveoli are produced allowing the fitting of one or moreamplification focusing devices 106 in the form of spheres.

According to the second embodiment depicted in FIG. 3, the receiver canbe an optical to electrical converter 304 adapted to receive theincident amplified electromagnetic wave 114 and to convert it into anelectrical signal 314 transported by an electric cable 302. The opticalto electrical converter 304 can for example be of the APD diode type(Avalanche Photodiode in English). Advantageously, a filter placedbetween the optical to electrical converter 304 and the amplificationfocusing device 106 makes it possible to select only the desiredincident wavelength or wavelengths from on the one hand the incidentamplified electromagnetic wave 114 and on the other hand the excitationwave 112.

Depending on the elements constituting the amplifying concentrator 100and the properties of the incident electromagnetic wave 116, thecoupling between the amplification focusing device 106 and the receiver102, 304 can be critical or non-critical.

The amplification focusing device 106 offers a maximum angular openingof 90°, directly dependent on the refractive index of the amplificationfocusing device 106.

In particular, the amplification focusing device 106 can take any formoffering an appropriate angular opening, such as for example a glasshemisphere or sphere.

Controlling the energy level of the excitation wave 112 affords directcontrol of the amplification level, that is to say of the level of thesignal detected. In general terms, a variation of the power of theexcitation wave 112 in one direction causes a variation of the power ofthe incident amplified wave 114 in the same direction, that is to say anincrease in the power of the excitation wave 112 will cause an increasein the number of photons emitted and therefore an increase in the powerof the incident amplified wave 114, whilst a reduction in the power ofthe excitation wave 112 will cause a reduction in the number of photonsemitted and therefore a reduction in the power of the incident amplifiedwave 114.

The photomultiplication thus achieved affords an amplification of theenergy that enters respectively the receiver 102, 304 and thereforebetter detection of the signal transported by the incident wave.

As material for the amplification focusing device 106, it will bepossible to use fluorinated, phosphate, silicate, titanate or otherglasses in the form of spheres with a diameter of around 100micrometers, and as active components it will be possible to use,depending on the wavelength of the incident electromagnetic wave,erbium, ytterbium, neodymium or other ions or a combination of theseelements.

These various characteristics and the concentration of the activecomponents 108 must be chosen according to their reactivity vis-à-visthe wavelengths of the incident electromagnetic wave 116 and so as toobtain an amplification effect without generating a laser effect; forexample, the concentration of the active components 108 will be around0.01 moles to 15 moles percent.

For example, in the case of an incident electromagnetic wave 116 lyingin the 1060-1100 nm band, use will be made of an amplification focusingdevice 106 made from fluorinated or silicate glass doped with neodymiumion at concentrations of between 0.01 moles to 15 moles percent.

The small dimensions of the various elements constituting the deviceguarantee a small overall size.

The use of a component based on glass guarantees high stability of thedevice vis-à-vis variations in temperature, and in fact these elementsare little sensitive to variations in temperature.

The excitation wave 112 can be a so-called pumping laser beam thatsupplies an addition of energy to the active components 108 of theamplification focusing device 106, thus exciting the active components108 and enabling them to pass to the higher energy level.

For example, for an incident electromagnetic wave 116 whose wavelengthis situated at approximately 1550 nm, the addition of energy supplied bythe excitation wave 112 will be approximately from a few microwatts to afew milliwatts for an amplification focusing device 106 and thewavelength of the excitation wave 112 will be around 980 nm or around1480 nm in the case of doping with the erbium ion, whose resonantfrequencies are situated at approximately 980 nm and 1480 nm or in thecase of an erbium/ytterbium co-doping whose resonant frequency is around980 nm.

The source of the emission of the excitation wave 112 can be placedanywhere with respect to the amplification focusing device 106, providedthat the excitation wave 112 illuminates the amplification focusingdevice 106. For reasons of saving in space, it is advantageous for thesource to be placed at the end of a waveguide adapted to conduct theexcitation wave 112 placed opposite the amplification focusing device106.

When the receiver is an optical to electrical converter 304, thewaveguide adapted to conduct the excitation wave 112 is an optical fibre102, preferably tapered to enable it to be fitted close to the opticalto electrical converter 304.

When the receiver is a waveguide, it is advantageous for the waveguideadapted to conduct the excitation wave 112 and the waveguide 102 adaptedto conduct the incident amplified electromagnetic wave 114 to be thesame. The excitation wave 112 is thus emitted towards the amplificationfocusing device 106 from the waveguide 102.

FIG. 2 depicts a device 200 for receiving an incident electromagneticwave comprising a plurality of amplifying concentrators 100 according tothe first embodiment and FIG. 4 depicts a device 400 for receiving anincident electromagnetic wave comprising a plurality of amplifyingconcentrators 300 according to the second embodiment and whose spatialdistribution makes it possible to cover a specific angular opening.

For example, in the case of an atmospheric optical connection, theincident electromagnetic wave generally has the form of a beam with asmall angle of dispersion and the amplifying concentrators 100, 300 mustbe located so as to cover only the incident beam without being able topick up the stray electromagnetic waves. The amplifying concentrators100, 300 will therefore be concentrated in a restricted region.

In the case of local networks, the incident electromagnetic wave isemitted in all directions with a large angle of dispersion and theamplifying concentrators 100, 300 must be able to pick up the maximumamount of energy issuing from this wave, whether it be directly or afterreflection. The arrangement of the amplifying concentrators 100, 300must then cover an extended angular opening, in particular 180°, and theamplification focusing devices 106 of the plurality of amplifyingconcentrators 100, 300 will be distributed over a surface 202, which maybe substantially hemispherical or other depending on the desiredamplification characteristics and the characteristics of the incidentwave.

An increase in the number of amplifying concentrators 100, 300 will giverise to an increase in the amplification. The density of the amplifyingconcentrators 100, 300 and their arrangement will be able to bedifferent according to the application and the amplifications necessary.

The reception device 200, 400 can also comprise an adder 212, 312connected to the plurality of receivers 102, 304 of the amplifyingconcentrators 100, 300 and adapted to add the energies of the signalsissuing from each receiver 102, 304.

In the case where the receivers are waveguides 102, the adder is anoptical adder 212 and the energies of the signals are the energies ofthe incident amplified electromagnetic waves 114. The inputs of theoptical adder 212 are connected with the waveguides 102 of the pluralityof amplifying concentrators 100. The optical adder 212 adds the energiesof the incident amplified electromagnetic waves 114 conducted by eachwaveguide 102, and its output can be injected into a coupler or ademultiplexer 204. The coupler or demultiplexer 204 can then beconnected on the one hand to a device 208 for measuring the energy ofthe wave output from the coupler 204 and on the other hand to anexcitation wave generator 206. The output of the measuring device 208can be injected into an optical to electrical converter 210 in the caseof a requirement for conversion of the light signal and the measuringdevice 208 can be connected to the generator 206 in order to control itspower.

The functioning of the reception device 200 is then as follows. Part ofthe incident wave is captured by the plurality of amplifyingconcentrators 100 and is amplified on passing through the amplificationfocusing devices 106. The waveguides 102 situated behind eachamplification focusing device 106 therefore receive, through one end, anamplified part 114 of the incident wave and conducted as far as anotherend. All these other ends are connected to the adder 212, which makes itpossible to generate a wave whose light energy is substantially equal tothe sum of the light energies of the electromagnetic wave parts 114transmitted by the waveguides 102.

The optical coupler or demultiplexer 204 connected to the output of theoptical adder 212 injects the excitation wave 112 issuing from thegenerator 206 into the waveguide 102. The power delivered by thegenerator 206 must be sufficient to supply all the amplificationfocusing devices 106.

The amplification generated by the active components 108 can give riseto the production of a wave whose optical energy is high and it is thenadvantageous to be able to control the energy level of the wave outputfrom the coupler 204. The device 208 measuring the energy of the waveoutput from the coupler 204 makes it possible to check this level withrespect to a maximum level and when the level exceeds the maximum levelthe measuring device 208 is able to reduce the power of the excitationwave 112 by acting on the generator 206. In a similar manner, when thelevel is less than a minimum level, the measuring device 208 is able toincrease the power of the excitation wave 112.

When the light signal is to be converted into an electrical signal, theoptical to electrical converter 210 is placed at the output of themeasuring device 208, but this optical to electrical converter 210 isunnecessary when the subsequent processing of the light signal iscarried out by an all-optical device.

Where the receivers are optical to electrical converters 304, the adderis an electrical adder 312 and the energies of the signals are theenergies of the electrical signals 314. The inputs of the electricaladder 312 are connected to the electrical cables 302 of the plurality ofamplifying concentrators 300. The electrical adder 312 creates anincident electrical signal by adding the electrical energies issuingfrom the optical to electrical converters 304 and representing theincident amplified electromagnetic waves 114 issuing from eachamplification focusing device 106. The output of the electrical adder312 can be injected on the one hand into a device 310 for processing theincident electrical signal and on the other hand into a device 308 formeasuring the energy of the incident electrical signal.

The reception device 400 comprises an optical demultiplexer 404 thatreceives as an input the excitation wave 112 emitted by the generator206 and emits part of the excitation wave 112 output in the direction ofthe plurality of waveguides adapted to conduct the excitation wave 112.

The measuring device 308 can be connected to the generator 206 in orderto control its power.

The functioning of the reception device 400 is then as follows. Part ofthe incident wave is captured by the plurality of amplifyingconcentrators 300 and amplified on passing through the amplificationfocusing devices 106, and is then converted into an electrical signal314 by means of the optical to electrical converters 304, which areconnected to the electrical adder 312 by means of the electric cables302.

The electrical adder 312 generates a signal whose energy level issubstantially equal to the sum of the energy levels of the electricalsignals 314 transmitted by the cables 312 from the optical to electricalconverters 304.

The demultiplexer 404 injects the excitation wave 112 issuing from thegenerator 206 into the waveguides 102. The power delivered by thegenerator 206 must be sufficient to supply all the amplificationfocusing devices 106.

The amplification generated by the active components 108 can give riseto the production of a wave whose optical energy is high and it is thenadvantageous to be able to control the energy level of the wave outputfrom the generator 206. The device 308 measuring the electrical energyoutput from the electrical adder makes it possible to check this levelwith respect to a maximum level and when the level exceeds the maximumlevel the measuring device 308 is able to reduce the power of theexcitation wave 112 by acting on the generator 206. In a similar manner,when the level is less than a minimum level, the measuring device 208 isable to increase the power of the excitation wave 112.

Naturally the present invention is not limited to the examples andembodiments described and depicted but is capable of many variantsaccessible to persons skilled in the art.

For example, the amplifying concentrator 100, 300 and the receptiondevice 200, 400 are not limited to the processing of an electromagneticwave with a single wavelength but can process waves with severalwavelengths.

It will then be possible to dope the amplification focusing device 106with several active components 108, each active component 108 beingadapted to at least one wavelength.

Amplifying concentrators 100, 300 adapted to each wavelength can also beinstalled in the reception device 200, 400.

The various components of the reception device 200 are shown as beingdistant from one another and connected by waveguides but they can alsobe mounted on one another in order to avoid insertion losses.

1. Amplifying optical electromagnetic wave concentrator comprising atleast one amplification focusing device and a receiver, theamplification focusing device being adapted to focus an incident opticalelectromagnetic wave on the receiver, the amplification focusing deviceincluding material doped with active components, an excitation wavesource for supplying electromagnetic energy to the amplificationfocusing device for causing the active components to pass to an energylevel such that interaction between the incident electromagnetic waveand the active components causes the active components to pass to alower energy level and causes emission of at least one photon having thesame wavelength as the incident electromagnetic wave towards thereceiver, whereby focused photon or photons adapted to be emitted by theactive components are in an amplified wave of the incidentelectromagnetic wave, the amplified wave being adapted to be incident onthe receiver.
 2. Amplifying concentrator according to claim 1, wherein apower variation of the excitation wave in one amplitude direction causesa variation of the power of the incident amplified wave in the sameamplitude direction.
 3. Amplifying concentrator according to claim 1,wherein the amplification focusing device has a spherical orhemispherical shape.
 4. Amplifying concentrator according to claim 1,wherein the receiver includes a waveguide adapted to conduct theincident amplified wave.
 5. Amplifying concentrator according to claim4, wherein the waveguide is an optical fibre.
 6. Amplifying concentratoraccording to claim 5, wherein the optical fibre has an end opposite theamplification focusing device that includes a microlens.
 7. Amplifyingconcentrator according to claim 5, further including a tubular device inwhich the optical fibre is positioned, the tubular device having an endwhere the amplification focusing device is located.
 8. Amplifyingconcentrator according to claim 4, wherein the waveguide is a planarguide.
 9. Amplifying concentrator according to claim 1, wherein thereceiver includes an optical to electrical converter.
 10. Amplifyingconcentrator according to claim 1, wherein the excitation wave source isa laser beam source.
 11. Amplifying concentrator according to claim 1,wherein the excitation wave is adapted to be emitted towards theamplification focusing device from a waveguide adapted to conduct theexcitation wave.
 12. Amplifying concentrator according to claim 4,wherein the excitation wave is adapted to be emitted towards theamplification focusing device from a waveguide adapted to conduct theexcitation wave, wherein the waveguide adapted to conduct the excitationwave is the waveguide adapted to conduct the incident amplified wave.13. Device for receiving an incident optical electromagnetic wavecomprising a plurality of amplifying concentrators according to claim 1.14. Reception device according to claim 13, wherein the amplificationfocusing devices of the plurality of amplifying concentrators aredistributed over a substantially hemispherical surface.
 15. Receptiondevice according to claim 13, further including an adder connected tothe plurality of receivers and adapted to add the signals issuing fromeach receiver.
 16. Reception device according to claim 15 wherein thereceivers include waveguides, the reception device including an opticalcoupler or a demultiplexer connected to the output of the optical adderand adapted to be responsive to the excitation wave.
 17. Receptiondevice according to claim 16, further including a device for measuringthe energy of the wave output from the optical coupler or from thedemultiplexer and a power controller arranged to be responsive to themeasuring device for controlling the power of the excitation wave. 18.Reception device according to claim 15 wherein the receivers includeoptical to electrical converters, the reception device including anoptical demultiplexer arranged to be responsive to the excitation waveand having outputs connected to the plurality of waveguides adapted toconduct the excitation wave.
 19. Reception device according to claim 18,further including a device for measuring the energy of the electricalsignal output from the electrical adder and a power controller arrangedto be responsive to the measuring device for controlling the power ofthe excitation wave.